The present invention relates generally to the detection of the presence of phase shift keyed (PSK) modulated signals using an instantaneous frequency measurement (IFM) receiver, particularly in a radar warning system.
Phase shift keyed (PSK) transmissions consist of phase modulating a carrier frequency in some coded manner. This type of modulation is one of the primary types which generically are referred to as spread spectrum transmissions. Spread spectrum radio frequency (RF) transmissions are used in radars to increase detectability and enhance their electronic counter-counter measures (ECCM) capability. Without specific knowledge of the carrier frequency, clock rate, and modulating code, the PSK transmission is extremely difficult to detect, characterize, and counter. In many radar EW (electronic warfare) applications, the lack of specific information about the signal is the normal operating environment.
One method of detecting a potential radar PSK transmission is discussed in a technical report AFWAL-TR-84-1014 (S) by M. B. Szymanski and R. G. Wiley titled "Spread Spectrum Receiver," February 1984. This approach employs a rapid scan superheterodyne receiver with noncoherent processing gain to detect a long pulse signal with a low signal to noise ratio imbedded in a background of standard radar signals and noise. The primary limitation of this approach is that the PSK signal must be a long pulse signal.
Another method of detecting a PSK signal is described in U. S. Patent 4,597,107 to Ready et al. This approach, while apparently feasible requires a special receiver/processor be built specifically to accomplish this. The advantage to this approach however is also the reported capability to detect low signal to noise transmissions.
Other U. S. Patents of interest include No. 4,166,980 to Apostolos et al, which discloses recognition of several signal types including PSK from compressive receivers. No. 4,227,255 to Carrick et al discloses a signal classifier. No. 4,298,985 to Ballard et al shows a digital filter bank detector. No. 4,612,545 to Asendorf et al discloses an automatic frequency identifier for radar signals, using an IFM receiver and an Instantaneous Fourier Transform receiver.